AVENGERS (1963) #54

Jarvis, Iron Man’s loyal butler, betrays the Avengers for the new Masters of Evil. The Black Knight attempts to warn the Avengers about the security breach. The Masters of Evil, led by the Crimson Cowl, attack the Avengers. It is revealed that there is a decoy Crimson Cowl that is actually the robot Ultron, and the real Crimson Cowl appears to be Jarvis! First appearance of Ultron